Golf ball having a non-yellowing cover

ABSTRACT

A golf ball with a cover composed of a thermosetting polyurethane that has increased resistance to yellowing is disclosed herein. The golf ball of the present invention is able to accomplish this by providing a cover composed of a thermosetting polyurethane material formed from a toluene diisocyanate prepolymer and a curative composed of 20 to 40 parts 4,4″-methylenebis-(3-chloro,2,6-diethyl)-aniline and 80 to 60 parts diethyl 2,4-toluenediamine. The cover is preferably formed over a core and boundary layer.

CROSS REFERENCES TO RELATED APPLICATIONS

The Present Application is a continuation-in-part application of U.S.patent application Ser. No. 09/562,782, filed on May 2, 2000, now U.S.Pat. No. 6,511,388, which is a divisional application of U.S. patentapplication Ser. No. 09/295,635, filed on Apr. 20, 1999, now U.S. Pat.No. 6,117,024.

FEDERAL RESEARCH STATEMENT

[Not Applicable]

BACKGROUND OF INVENTION

1. Field of the Invention

The present invention relates to a cover for a golf ball. Morespecifically, the present invention relates to a golf ball cover layercomposed of a thermosetting polyurethane.

2. Description of the Related Art

Conventionally golf balls are made by molding a cover around a core. Thecore may be wound or solid. A wound core typically comprises elasticthread wound about a solid or liquid center. Unlike wound cores, solidcores do not include a wound elastic thread layer. Solid cores typicallymay comprise a single solid piece center or a solid center covered byone or more mantle or boundary layers of material.

The cover may be injection molded, compression molded, or cast over thecore. Injection molding typically requires a mold having at least onepair of mold cavities, e.g., a first mold cavity and a second moldcavity, which mate to form a spherical recess. In addition, a mold mayinclude more than one mold cavity pair.

In one exemplary injection molding process each mold cavity may alsoinclude retractable positioning pins to hold the core in the sphericalcenter of the mold cavity pair. Once the core is positioned in the firstmold cavity, the respective second mold cavity is mated to the first toclose the mold. A cover material is then injected into the closed mold.The positioning pins are retracted while the cover material is flowableto allow the material to fill in any holes caused by the pins. When thematerial is at least partially cured, the covered core is removed fromthe mold.

As with injection molding, compression molds typically include multiplepairs of mold cavities, each pair comprising first and second moldcavities that mate to form a spherical recess. In one exemplarycompression molding process, a cover material is pre-formed intohalf-shells, which are placed into a respective pair of compression moldcavities. The core is placed between the cover material half-shells andthe mold is closed. The core and cover combination is then exposed toheat and pressure, which cause the cover half-shells to combine and forma full cover.

As with the above-referenced processes, a casting process also utilizespairs of mold cavities. In a casting process, a cover material isintroduced into a first mold cavity of each pair. Then, a core is heldin position (e.g. by an overhanging vacuum or suction apparatus) tocontact the cover material in what will be the spherical center of themold cavity pair. Once the cover material is at least partially cured(e.g., a point where the core will not substantially move), the core isreleased, the cover material is introduced into a second mold cavity ofeach pair, and the mold is closed. The closed mold is then subjected toheat and pressure to cure the cover material thereby forming a cover onthe core. With injection molding, compression molding, and casting, themolding cavities typically include a negative dimple pattern to impart adimple pattern on the cover during the molding process.

Materials previously used as golf ball covers include balata (natural orsynthetic), gutta-percha, ionomeric resins (e.g., DuPont's SURLYN®), andpolyurethanes. Balata is the benchmark cover material with respect tosound (i.e. the sound made when the ball is hit by a golf club) and feel(i.e. the sensation imparted to the golfer when hitting the ball).Natural balata is derived from the Bully Gum tree, while syntheticbalata is derived from a petroleum compound. Balata is expensivecompared to other cover materials, and golf balls covered with balatatend to have poor durability (i.e. poor cut and shear resistance). Guttapercha is derived from the Malaysian sapodilla tree. A golf ball coveredwith gutta percha is considered to have a harsh sound and feel ascompared to balata covered golf balls.

Ionomeric resins, as compared to balata, are typically less expensiveand tend to have good durability. However, golf balls having ionomericresin covers typically have inferior sound and feel, especially ascompared to balata covers.

A golf ball with a polyurethane cover generally has greater durabilitythan a golf ball with a balata cover. The polyurethane covered golf ballgenerally has a better sound and feel than a golf ball with an ionomericresin cover. Polyurethanes may be thermoset or thermoplastic.Polyurethanes are formed by reacting a prepolymer with a polyfunctionalcuring agent, such as a polyamine or a polyol. The polyurethaneprepolymer is the reaction product of, for example, a diisocyanate and apolyol such as a polyether or a polyester. Several patents describe theuse of polyurethanes in golf balls. However, golf balls withpolyurethane covers usually do not have the distance of other golf ballssuch as those with covers composed of SURLYN® materials.

Gallagher, U.S. Pat. No. 3,034,791 discloses a polyurethane golf ballcover prepared from the reaction product of poly(tetramethylene ether)glycol and toluene-2,4-diisocyanates (TDI), either pure TDI or anisomeric mixture.

Isaac, U.S. Pat. No. 3,989,568 (the “568 patent) discloses apolyurethane golf ball cover prepared from prepolymers and curing agentsthat have different rates of reaction so a partial cure can be made. The“568 patent explains that the minimum number of reactants is three.Specifically, in “568 patent, two or more polyurethane prepolymers arereacted with at least one curing agent, or at least one polyurethaneprepolymer is reacted with two or more curing agents as long as thecuring agents have different rates of reaction. The “568 patent alsoexplains that [o]ne of the great advantages of polyurethane covers madein accordance with the instant invention is that they may be made verythin . . . , and [t]here is no limitation on how thick the cover of thepresent invention may be but it is generally preferred . . . that thecover is no more than about 0.6 inches in thickness. The examples in the“568 patent only disclose golf balls having covers that are about 0.025inches thick.

Similar to Isaac, PCT International Publication Number WO 99/43394 toDunlop Maxfli Sports Corporation, discloses using two curing agents tocontrol the reaction time for polyurethane formation. The two curingagents are a dimethylthio 2,4-toluenediamine and diethyl2,4-toluenediamine, which are blended to control the reaction rate of atoluene diisocyanate based polyurethane prepolymer or a4,4″-diphenylmethane diisocyanate based polyurethane prepolymer.

Dusbiber, U.S. Pat. No. 4,123,061 (the “061 patent) discloses apolyurethane golf ball cover prepared from the reaction product of apolyether, a diisocyanate and a curing agent. The “061 patent disclosesthat the polyether may be polyalkylene ether glycol orpolytetramethylene ether glycol. The “061 patent also discloses that thediisocyanate may be TDI, 4,4″-diphenylmethane diisocyanate (MDI), and3,3″-dimethyl-4,4″-biphenylene diisocyanate (TODI). Additionally, the“061 patent discloses that the curing agent may be either a polyol(either tri- or tetra-functional and not di-functional) such astriisopropanol amine (TIPA) or trimethoylol propane (TMP), or anamine-type having at least two reactive amine groups such as: 3,3″dichlorobenzidene; 3,3″ dichloro 4,4″ diamino diphenyl methane (MOCA);N,N,N″,N″ tetrakis (2-hydroxy propyl) ethylene diamine; or Uniroyal'sCuralon L which is an aromatic diamine mixture.

Hewitt, et al., U.S. Pat. No. 4,248,432 (the “432 patent) discloses athermoplastic polyesterurethane golf ball cover formed from a reactionproduct of a polyester glycol (molecular weight of 800-1500) (aliphaticdiol and an aliphatic dicarboxylic acid) with a para-phenylenediisocyanate (PPDI) or cyclohexane diisocyanate in the substantialabsence of curing or crosslinking agents. The “432 patent teachesagainst the use of chain extenders in making polyurethanes. The “432patent states, when small amounts of butanediol-1,4 are mixed with apolyester . . . the addition results in polyurethanes that do not havethe desired balance of properties to provide good golf ball covers.Similarly, the use of curing or crosslinking agents is not desired . . .

Holloway, U.S. Pat. No. 4,349,657 (the “657 patent) discloses a methodfor preparing polyester urethanes with PPDI by reacting a polyester(e.g. prepared from aliphatic glycols having 2-8 carbons reacted withaliphatic dicarboxylic acids having 4-10 carbons) with a molar excess ofPPDI to obtain an isocyanate-terminated polyester urethane (in liquidform and stable at reaction temperatures), and then reacting thepolyester urethane with additional polyester. The “657 patent claimsthat the benefit of this new process is the fact that a continuouscommercial process is possible without stability problems. The “657patent further describes a suitable use for the resultant material to begolf ball covers.

Wu, U.S. Pat. No. 5,334,673 (the “673 patent) discloses a polyurethaneprepolymer cured with a slow-reacting curing agent selected fromslow-reacting polyamine curing agents and difunctional glycols (i.e.,3,5-dimethylthio-2,4-toluenediamine,3,5-dimethylthio-2,6-toluenediamine, N,N″-dialkyldiamino diphenylmethane, trimethyleneglycol-di-p-aminobenzoate,polytetramethyleneoxide-di-p-aminobenzoate, 1,4-butanediol,2,3-butanediol, 2,3-dimethyl-2,3-butanediol, ethylene glycol, andmixtures of the same). The polyurethane prepolymer in the “673 patent isdisclosed as made from a polyol (e.g., polyether, polyester, orpolylactone) and a diisocyanate such as MDI or TODI. The polyetherpolyols disclosed in the “673 patent are polytetramethylene etherglycol, poly(oxypropylene) glycol, and polybutadiene glycol. Thepolyester polyols disclosed in the “673 patent are polyethylene adipateglycol, polyethylene propylene adipate glycol, and polybutylene adipateglycol. The polylactone polyols disclosed in the “673 patent arediethylene glycol initiated caprolactone, 1,4-butanediol initiatedcaprolactone, trimethylol propane initiated caprolactone, and neopentylglycol initiated caprolactone.

Cavallaro, et al., U.S. Pat. No. 5,688,191 discloses a golf ball havingcore, mantle layer and cover, wherein the mantle layer is either avulcanized thermoplastic elastomer, functionalized styrene-butadieneelastomer, thermoplastic polyurethane, metallocene polymer or blends ofthe same and thermoset materials.

Wu, et al., U.S. Pat. No. 5,692,974 discloses golf balls having coversand cores that incorporate urethane ionomers (i.e. using an alkylatingagent to introduce ionic interactions in the polyurethane and therebyproduce cationic type ionomers).

Sullivan, et al., U.S. Pat. No. 5,803,831 (the “831 patent) discloses agolf ball having a multi-layer cover wherein the inner cover layer has ahardness of at least 65 Shore D and the outer cover layer has a hardnessof 55 Shore D or less, and more preferably 48 Shore D or less. The “831patent explains that this dual layer construction provides a golf ballhaving soft feel and high spin on short shots, and good distance andaverage spin on long shots. The “831 patent provides that the innercover layer can be made from high or low acid ionomers such as SURLYN®,ESCOR® or IOTEK®, or blends of the same, nonionomeric thermoplasticmaterial such as metallocene catalyzed polyolefins or polyamides,polyamide/ionomer blends, polyphenylene ether/ionomer blends, etc.,(having a Shore D hardness of at least 60 and a flex modulus of morethan 30000 psi), thermoplastic or thermosetting polyurethanes, polyesterelastomers (e.g. HYTREL®), or polyether block amides (e.g. PEBAX®), orblends of these materials. The “831 patent also provides that the outercover layer can be made from soft low modulus (i.e. 1000-10000 psi)material such as low-acid ionomers, ionomeric blends, non-ionomericthermoplastic or thermosetting materials such as polyolefins,polyurethane (e.g. thermoplastic polyurethanes like TEXIN®, PELETHANE®,and thermoset polyurethanes like those disclosed in Wu, U.S. Pat. No.5,334,673), polyester elastomer (e.g. HYTREL®), or polyether block amide(e.g. PEBAX®), or a blend of these materials.

Hebert, et al., U.S. Pat. No. 5,885,172 (the “172 patent) discloses amultilayer golf ball giving a progressive performance (i.e. differentperformance characteristics when struck with different clubs atdifferent head speeds and loft angles) and having an outer cover layerformed of a thermoset material with a thickness of less than 0.05 inchesand an inner cover layer formed of a high flexural modulus material. The“172 patent provides that the outer cover is made from polyurethaneionomers as described in Wu, et al., U.S. Pat. No. 5,692,974, orthermoset polyurethanes such as TDI or methylenebis-(4-cyclohexylisocyanate) (HMDI), or a polyol cured with a polyamine (e.g.methylenedianiline (MDA)), or with a trifunctional glycol (e.g.,N,N,N″,N″-tetrakis(2-hydroxpropyl)ethylenediamine). The “172 alsoprovides that the inner cover has a Shore D hardness of 65-80, aflexural modulus of at least about 65,000 psi, and a thickness of about0.020-0.045 inches. Exemplary materials for the inner cover areionomers, polyurethanes, polyetheresters (e.g. HYTREL®), polyetheramides(e.g., PEBAX®), polyesters, dynamically vulcanized elastomers,functionalized styrene-butadiene elastomer, metallocene polymer, blendsof these materials, nylon or acrylonitrile-butadiene-styrene copolymer.

Wu, U.S. Pat. No. 5,484,870 (the “870 patent) discloses golf ballshaving covers composed of a polyurea composition. The polyureacomposition disclosed in the “870 patent is a reaction product of anorganic isocyanate having at least two functional groups and an organicamine having at least two functional groups. One of the organicisocyanates disclosed by the “870 patent is PPDI.

Although the prior art has disclosed golf ball covers composed of manydifferent polyurethane materials, none of these golf balls have provencompletely satisfactory. One particular dissatisfaction has been theyellowing of thermosetting polyurethane covers upon exposure to sunlight(ultraviolet radiation). Thus, there remains a need for thermosettingpolyurethane covers that have reduced yellowing while maintaining theother desired properties of a thermosetting polyurethane cover.

SUMMARY OF INVENTION

The present invention provides a golf ball that has a cover composed ofa thermosetting polyurethane that has increased resistance to yellowing.The golf ball of the present invention is able to accomplish this byproviding a cover composed of a thermosetting polyurethane materialformed from a toluene diisocyanate prepolymer and a curative composed of20 to 40 parts 4,4″-methylenebis-(3-chloro,2,6-diethyl)-aniline and 80to 60 parts diethyl 2,4-toluenediamine.

One aspect of the present invention is a golf ball including a core anda cover. The cover is composed of a thermosetting polyurethane materialformed from reactants including a polypropylene glycol terminatedtoluene diisocyanate prepolymer and 4,4″-methylenebis-(3-chloro,2,6-diethyl)-aniline. The cover has an aerodynamic surface geometrythereon.

Another aspect of the present invention is a golf ball including a core,a boundary layer and a cover. The core is a polybutadiene mixture andhas a diameter ranging from 1.35 inches to 1.64 inches. The core alsohas a PGA compression ranging from 50 to 90. The boundary layer isformed over the core and is composed of a blend of ionomer materials.The boundary layer has a thickness ranging from 0.020 inch to 0.075 inchand a Shore D hardness ranging from 50 to 75 as measured according toASTM-D2240. The cover is formed over the boundary layer. The cover iscomposed of a thermosetting polyurethane material formed from reactantsincluding a polypropylene glycol terminated toluene diisocyanateprepolymer and a curative composed of 20 to 40 parts4,4′-methylenebis-(3-chloro,2,6-diethyl) -aniline and 80 to 60 partsdiethyl 2,4-toluenediamine. The cover has a Shore D hardness rangingfrom 30 to 60 as measured according to ASTM-D2240. The cover also has athickness ranging from 0.015 inch to 0.040 inch and an aerodynamicsurface geometry thereon. The golf ball may have a PGA compressionranging from 70 points to 100 points.

Having briefly described the present invention, the above and furtherobjects, features and advantages thereof will be recognized by thoseskilled in the pertinent art from the following detailed description ofthe invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a perspective view of a golf ball of the presentinvention including a cut-away portion showing a core, a boundary layer,and a cover.

FIG. 2 illustrates a perspective view of a golf ball of the presentinvention including a cut-away portion core and a cover.

DETAILED DESCRIPTION

As illustrated in FIG. 1, the golf ball of the present invention isgenerally indicated as 10. The golf ball 10 includes a core 12, aboundary layer 14 and a cover 16. Alternatively, as shown in FIG. 2, thegolf ball 10 may only include a core 12 and a cover 16. The cover 16 ispreferably composed of a thermosetting polyurethane material formed froma toluene diisocyanate prepolymer and4,4″-methylenebis-(3-chloro,2,6-diethyl)-aniline. In a preferredembodiment, the cover 16 is formed over a boundary layer 14 and core 12,as shown in FIG. 1. Alternatively, the cover 16 is formed over the core12, as shown in FIG. 2. Those skilled in the art will recognize that thecore may be solid, hollow, multi-piece or liquid-filled, and theboundary layer may be partitioned into additional layers, withoutdeparting from the scope and spirit of the present invention.

As mentioned above, the thermosetting polyurethane material is formedfrom a toluene diisocyanate prepolymer and a curative composed of a4,4″-methylenebis-(3-chloro,2,6-diethyl)-aniline. The toluenediisocyanate prepolymer is preferably a polypropylene glycol terminatedtoluene diisocyanate prepolymer or a polytetramethylene ether glycolterminated toluene diisocyanate prepolymer. In a further embodiment, thethermosetting polyurethane material is formed from a polypropyleneglycol terminated toluene diisocyanate prepolymer and a curativecomposed of 4,4″-methylenebis-(3-chloro,2,6-diethyl)-aniline and diethyl2,4-toluenediamine. A preferred polypropylene glycol terminated toluenediisocyanate prepolymer is available from Uniroyal Chemical Company ofMiddlebury, Conn., under the tradename ADIPRENE® LFG960. A preferredpolytetramethylene ether glycol terminated toluene diisocyanateprepolymer is available from Uniroyal Chemical Company of Middlebury,Conn., under the tradename ADIPRENE® LF930. Diethyl 2,4-toluenediamineis available from Albemarle Corporation of Baton Rouge, La. under thetradename ETHACURE® 100. 4,4″-methylenebis-(3-chloro,2,6-diethyl)-aniline is available from Air Products and Chemicals Inc.,of Allentown, Pa., under the tradename LONZACURE™.

The curative mixture for the cover 16 may have numerous variations. Thecurative mixture includes4,4″-methylenebis-(3-chloro,2,6-diethyl)-aniline in order to control thereaction time and to affect the diminished yellowing of the cover afterexposure to sunlight. In a preferred embodiment, the curative mixture iscomposed of 20 to 40 parts4,4″-methylenebis-(3-chloro,2,6-diethyl)-aniline and 80 to 60 partsdiethyl 2,4-toluenediamine. A most preferred curative mixture iscomposed of 30 parts 4,4″-methylenebis-(3-chloro,2,6-diethyl)-anilineand 70 parts diethyl 2,4-toluenediamine.

The ratio of the polyurethane prepolymer to curative is determined bythe nitrogen-carbon-oxygen group (NCO) content of the polyurethaneprepolymer. For example, the NCO content of the polypropylene glycolterminated toluene diisocyanate prepolymer is preferably in the range of3.0% to 6.0%, more preferably in the range of 4.0% to 5.75%, and mostpreferably 5.70%. The NCO content of the polytetramethylene ether glycolterminated toluene diisocyanate prepolymer is preferably in the range of3.75% to 7.0%, more preferably in the range of 4.0% to 5.75%, and mostpreferably 5.70%. The weight ratio of the polyurethane prepolymer to thecurative is preferably in the range of about 10:1 to about 30:1.

Prior to curing, the polyurethane prepolymer and curative are preferablystored separately. The polyurethane material is formed by first heatingand mixing the polyurethane prepolymer with the curative in a mold, andthen curing the mixture by applying heat and pressure for apredetermined time period. Additionally, a catalyst (e.g. dibutyl tindilaurate, a tertiary amine, etc.) may be added to the mixture toexpedite the casting process. Specific suitable catalysts include TEDAdissolved in di propylene glycol (such as TEDA L33 available from WitcoCorp. Greenwich, Conn., and DABCO 33 LV available from Air Products andChemicals Inc.,) which may be added in amounts of 2-5%, and morepreferably TEDA dissolved in 1,4-butane diol which may be added inamounts of 2-5%. Another suitable catalyst includes a blend of 0.5% 33LVor TEDA L33 (above) with 0.1% dibutyl tin dilaurate (available fromWitco Corp. or Air Products and Chemicals, Inc.) which is added to acurative such as VIBRACURE® A250. Furthermore, additives such ascolorants may also be added to the mixture.

The polyurethane prepolymer is preferably degassed and warmed in a firstholding container prior to processing of the cover 16. The processingtemperature for the polyurethane prepolymer is preferably in the rangeof about 100-220° F., and most preferably in the range of about 120-200°F. The polyurethane prepolymer is preferably flowable from the firstholding container to a mixing chamber in a range of about 200-1100 gramsof material per minute, or as needed for processing. In addition, thepolyurethane prepolymer material may be agitated in the first holdingcontainer, in the range of 0-250 rpm, to maintain a more evendistribution of material and to eliminate crystallization.

The curative is preferably degassed and warmed in a second holdingcontainer prior to processing of the cover 16. The processingtemperature for the curative is preferably in the range of about 50-230°F., and most preferably in the range of about 80-200° F. The curative ispreferably flowable from the second holding container to the mixingchamber in the range of about 15-75 grams of material per minute, or asneeded. If a catalyst is used for processing the cover 16, then thecatalyst is added to the curing agent in the second holding container toform a curative mixture. Suitable catalyst are described above. Thecurative and catalyst are agitated, in the range of about 0 to 250 rpm,to maintain an even distribution of catalyst in the curative mixture inthe second holding container. It is preferred that the catalyst is addedin an amount in the range of about 0.25-5% by weight of the combinedpolyurethane prepolymer and curative. Additives may be added to thecurative mixture as desired. It was discovered that hydrolyticinstability of the polyurethane polymer may be avoided by the additionof a stabilizer such as STABOXYL® (available from Rheinchemie, Trenton,N.J.), in amounts of about 0.25-5% of the polyurethane.

The polyurethane prepolymer and curative mixture are preferably added tothe common mixing chamber at a temperature in the range of about160-220° F. A colorant material, such as, for example, titanium dioxide,barium sulfate, and/or zinc oxide in a glycol or castor oil carrier,and/or other additive material(s) as are well known in the art, may beadded to the common mixing chamber. The amount of colorant materialadded is preferably in the range of about 0-10% by weight of thecombined polyurethane prepolymer and curative materials, and morepreferably in the range of about 2-8%. Other additives, such as, forexample, polymer fillers, metallic fillers, and/or organic and inorganicfillers (e.g. polymers, balata, ionomers, etc.) may be added as well toincrease the specific gravity of the polyurethane cover 16 of thepresent invention. It was discovered that the addition of barytes(barium sulfate) or a blend of barytes and titanium dioxide (preferablyadded in a carrier glycol and/or castor oil) to the mixture, in theamounts of about 0.01-30%, may add sufficient weight to the polyurethanecover 16. The added weight to the cover 16 allows for a lower specificgravity for the core 12 thereby allowing for an increased resiliency ofthe core 12. The entire mixture is preferably agitated in the mixingchamber in the range of about 1 to 250 rpm prior to molding. A moredetailed explanation of the process is set forth in U.S. Pat. No.6,200,512, entitled Golf Balls And Methods Of Manufacturing The Same,filed on Apr. 20, 1999, assigned to Callaway Golf Company, and which ishereby incorporated by reference in its entirety.

The core 12 of the golf ball 10 is the engine for the golf ball 10 suchthat the inherent properties of the core 12 will strongly determine theinitial velocity and distance of the golf ball 10. A higher initialvelocity will usually result in a greater overall distance for a golfball. In this regard, the Rules of Golf, approved by the United StatesGolf Association (USGA) and The Royal and Ancient Golf Club of SaintAndrews, limits the initial velocity of a golf ball to 250 feet (76.2 m)per second (a two percent maximum tolerance allows for an initialvelocity of 255 per second) and the overall distance to 280 yards (256m) plus a six percent tolerance for a total distance of 296.8 yards (thesix percent tolerance may be lowered to four percent). A completedescription of the Rules of Golf are available on the USGA web page atwww.usga.org. Thus, the initial velocity and overall distance of a golfball must not exceed these limits in order to conform to the Rules ofGolf. Therefore, the core 12 for a USGA approved golf ball isconstructed to enable the golf ball 10 to meet, yet not exceed, theselimits.

The coefficient of restitution (COR) is a measure of the resilience of agolf ball. The COR is a measure of the ratio of the relative velocity ofthe golf ball after direct impact with a hard surface to the relativevelocity before impact with the hard surface. The COR may vary from 0 to1, with 1 equivalent to a completely elastic collision and 0 equivalentto a completely inelastic collision. A golf ball having a COR valuecloser to 1 will generally correspond to a golf ball having a higherinitial velocity and a greater overall distance. If the golf ball has ahigh COR (more elastic), then the initial velocity of the golf ball willbe greater than if the golf ball had a low COR. In general, a highercompression core will result in a higher COR value.

The core 12 of the golf ball 10 is generally composed of a blend of abase rubber, a cross-linking agent, a free radical initiator, and one ormore fillers or processing aids. A preferred base rubber is apolybutadiene having a cis-1,4 content above 90%, and more preferably98% or above.

The use of cross-linking agents in a golf ball core is well known, andmetal acrylate salts are examples of such cross-linking agents. Forexample, metal salt diacrylates, dimethacrylates, or mono(meth)acrylatesare preferred for use in the golf ball cores of present invention, andzinc diacrylate is a particularly preferred cross-linking agent. Acommercially available suitable zinc diacrylate is SR-416 available fromSartomer Co., Inc., Exton, Pa. Other metal salt di- or mono-(meth)acrylates suitable for use in the present invention include thosein which the metal is calcium or magnesium. In the manufacturing processit may be beneficial to pre-mix some cross-linking agent(s), such as,e.g., zinc diacrylate, with the polybutadiene in a master batch prior toblending with other core components.

Free radical initiators are used to promote cross-linking of the baserubber and the cross-linking agent. Suitable free radical initiators foruse in the golf ball core 12 of the present invention include peroxidessuch as dicumyl peroxide, bis-(t-butyl) peroxy) diisopropyl benzene,t-butyl perbenzoate, di-t-butyl peroxide,2,5-dimethyl-2,5-di-5-butylperoxy-hexane, 1,1-di (t-butylperoxy)3,3,5-trimethyl cyclohexane, and the like, all of which are readilycommercially available.

Zinc oxide is also preferably included in the core formulation. Zincoxide may primarily be used as a weight adjusting filler, and is alsobelieved to participate in the cross-linking of the other components ofthe core (e.g. as a coagent). Additional processing aids such asdispersants and activators may optionally be included. In particular,zinc stearate may be added as a processing aid (e.g. as an activator).Any of a number of specific gravity adjusting fillers may be included toobtain a preferred total weight of the core 12. Examples of such fillersinclude tungsten and barium sulfate. All such processing aids andfillers are readily commercially available. The present inventors havefound a particularly useful tungsten filler is WP102 Tungsten (having a3 micron particle size) available from Atlantic Equipment Engineers (adivision of Micron Metals, Inc.), Bergenfield, N.J.

Table One below provides the ranges of materials included in thepreferred core formulations of the present invention.

TABLE ONE Component Preferred Range Most Preferred Range Polybutadiene100 parts 100 parts Zinc diacrylate 20-35 phr 25-30 phr Zinc oxide 0-50phr 5-15 phr Zinc stearate 0-15 phr 1-10 phr Peroxide 0.2-2.5 phr0.5-1.5 phr Filler As desired As desired (e.g. tungsten) (e.g. 2-10 phr)(e.g. 2-10 phr)

In the present invention, the core components are mixed and compressionmolded in a conventional manner known to those skilled in the art. In apreferred form, the finished core 12 has a diameter of about 1.35 toabout 1.64 inches for a golf ball 10 having an outer diameter of 1.68inches. The core weight is preferably maintained in the range of about32 to about 40 g. The core PGA compression is preferably maintained inthe range of about 50 to 90, and most preferably about 55 to 80.

As used herein, the term PGA compression is defined as follows:

PGA compression value=180 Riehle compression value

The Riehle compression value is the amount of deformation of a golf ballin inches under a static load of 200 pounds, multiplied by 1000.Accordingly, for a deformation of 0.095 inches under a load of 200pounds, the Riehle compression value is 95 and the PGA compression valueis 85.

As is described above, the present invention preferably includes atleast one boundary layer 14 that preferably is composed of athermoplastic (e.g. thermoplastic or thermoplastic elastomer) or a blendof thermoplastics (e.g. metal containing, non-metal containing or both).However, the golf ball 10 may have several boundary layers 14 disposedbetween the core 12 and the cover 16. Most preferably the boundary layer14 is composed of at least one thermoplastic that contains organic chainmolecules and metal ions. The metal ion may be, for example, sodium,zinc, magnesium, lithium, potassium, cesium, or any polar metal ion thatserves as a reversible cross-linking site and results in high levels ofresilience and impact resistance. Suitable commercially availablethermoplastics are ionomers based on ethylene copolymers and containingcarboxylic acid groups with metal ions such as described above. The acidlevels in such suitable ionomers may be neutralized to controlresiliency, impact resistance and other like properties. In addition,other fillers with ionomer carriers may be used to modify (e.g.preferably increase) the specific gravity of the thermoplastic blend tocontrol the moment of inertia and other like properties. Exemplarycommercially available thermoplastic materials suitable for use in aboundary layer 14 of a golf ball 10 of the present invention include,for example, the following materials and/or blends of the followingmaterials: HYTREL® and/or HYLENE® products from DuPont, Wilmington,Del., PEBAX® products from Elf Atochem, Philadelphia, Pa., SURLYN®products from DuPont, and/or ESCOR® or IOTEK® products from ExxonChemical, Houston, Tex.

The Shore D hardness of the boundary layer 14 ranges from 50 to 75, asmeasured according to ASTM D-2290. It is preferred that the boundarylayer 14 have a hardness of between about 55-70 Shore D. In a preferredembodiment, the boundary layer 14 has a Shore D hardness in the range of58-65. One reason for preferring a boundary layer 14 with a Shore Dhardness of 75 or lower is to improve the feel of the resultant golfball. It is also preferred that the boundary layer 14 is composed of ablend of SURLYN® ionomer resins. SURLYN® 8150, 9150, and 6320 are,respectively, an ionomer resin composed of a sodium neutralizedethylene/methacrylic acid, an ionomer resin composed of a zincneutralized ethylene/methacrylic acid, and an ionomer resin composed ofa terpolymer of ethylene, methacrylic acid and n-butyl acrylatepartially neutralized with magnesium, all of which are available fromDuPont, Polymer Products, Wilmington, Del.

Exemplary golf balls of the present invention were constructed andcompared to the CALLAWAY GOLF RULE 35 FIRMFEEL golf ball. Table Two andTable Three set forth the physical properties of the exemplary group ofgolf balls #1, #2 and #3. A dozen golf balls were constructed for eachgroup #1, #2 and #3. Each of the boundary layers 14 of the exemplarygolf balls #1, #2 and #3 were composed of an ionomer blend of forty-fiveweight percent SURLYN 8150, forty-five weight percent SURLYN 9150 andten weight percent SURLYN 6350. The average thickness of each of theboundary layers 14 of the exemplary golf balls #1, #2 and #3 was 0.0525inch. The Shore D hardness of the boundary layer 14 of the exemplarygolf balls #1, #2 and #3 was 62 points. The Shore D hardness provided inTable Three below was determined according to ASTM D2240.

Each of the covers 16 of the exemplary group of golf balls #1, #2 and #3were composed of a polytetramethylene ether glycol terminated toluenediisocyanate prepolymer (ADRIPRENE LF930) cured with a blend of seventyweight percent diethyl 2,4-toluenediamine (E100) and thirty weightpercent 4,4″-methylenebis-(3-chloro,2,6-diethyl)-aniline (LONZACURE).The average thickness of each of the covers 16 of the exemplary golfballs #1, #2 and #3 was 0.030 inch. The Shore D hardness of the covers16 of the exemplary golf balls #1, #2 and #3 was 51 points. The COR at143 feet per second of each of the exemplary golf balls #1, #2 and #3was 79.42 points.

TABLE TWO Bound. Layer Cover Bound. Layer Cover Shore D Shore DThickness Thickness COR Ball (points) (points) (inch) (inch) (points)Ball 1 62 51 0.0525 0.030 79.42 2 62 51 0.0525 0.030 79.42 3 62 510.0525 0.030 79.42

The average weight of each of the exemplary golf balls #1, #2 and #3 was45.29 grams. The PGA compression of each of the exemplary golf balls #1,#2 and #3 was 95. The average diameter of each of the exemplary golfballs #1, #2 and #3 was 1.683 inch. The core diameter of each of thecores 12 of each of the exemplary golf balls #1, #2 and #3 was 1.515inches. The PGA compression of each of the cores 12 of each of theexemplary golf balls #1, #2 and #3 was 70 points.

TABLE THREE Ball Ball Weight Compression Average Core (grams) (inches)Diameter Core Ball (points) (inches) (points) Diameter Compression 145.29 95 1.683 1.515 70 2 45.29 95 1.683 1.515 70 3 45.29 95 1.683 1.51570

Tables Four, Five, Six, Seven, Eight and Nine compare the CALLAWAY GOLFRULE 35 FIRMFEEL golf ball to the exemplary golf balls #1, #2 and #3 ofthe present invention. The golf balls were measured to determine theyellowing of the thermosetting polyurethane covers after exposure tosunlight. The color of the cover of each of the golf balls is determinedusing a HUNTER COLORIMETER model ULTRA SCAN XE and measuring the coloron a L.a. b. scale. On the L scale, a measurement of 100 corresponds tocomplete white while a measurement of 0 corresponds to complete black.On the a scale, a negative number corresponds to a green color while apositive number corresponds to a red color. On the b scale, a negativenumber corresponds to a blue color while a positive number correspondsto a yellow color. Thus, the more positive the b measurement, the moreyellow the cover. The golf balls were measured before exposure tosunlight, after four hours of exposure to sunlight and after twenty-fourhours of exposure to sunlight/night. The average of the CALLAWAY GOLFRULE 35 FIRMFEEL golf balls after four hours of exposure to sunlight isset forth in Table Five. The average of the exemplary golf balls #1, #2and #3 of the present invention after four hours of exposure to sunlightis set forth in Table Six. The average of the CALLAWAY GOLF RULE 35FIRMFEEL golf balls after twenty-four hours of exposure tosunlight/night is set forth in Table Eight. The average of the exemplarygolf balls #1, #2 and #3 of the present invention after twenty-fourhours of exposure to sunlight is set forth in Table Nine.

TABLE FOUR Before After 4 Exposure Hour Exposure Difference Ball L a* b*L A* b* L a* b* Rule 93.2 −1.26 9.07 75.94 7.91 38.22 −17.26 9.17 29.1535 Firm #1 Rule 93.15 −1.24 9.18 76.77 7.3 38.42 −16.38 8.54 29.24 35Firm #2 Rule 93.03 −1.28 8.88 76.65 7.11 37.81 −16.38 8.39 28.93 35 Firm#3 Ex. 1 95.09 −1.5 2.04 83.09 0.27 21.18 −12 1.77 19.14 Ex. 2 95.12−1.51 2.19 85.57 −0.47 19.16 −9.55 1.04 16.97 Ex. 3 95.55 −1.52 2.689.12 −1.44 15.78 −6.43 0.08 13.18

TABLE FIVE Average for RULE 35 Balls L a* b* DE −16.67 8.70 29.11 34.65

TABLE SIX Average for Exemplary Balls of the Present Invention L a* b*DE −9.33 0.96 16.43 18.92

TABLE SEVEN Before After 24 Exposure Hour Exposure Difference Ball L a*b* L a* b* L a* b* Rule 93.2 −1.26 9.07 69.42 13.12 40.59 −23.78 14.3831.52 35 Firm #1 Rule 93.15 −1.24 9.18 69.71 12.85 40.53 −23.44 14.0931.35 35 Firm #2 Rule 93.03 −1.28 8.88 70.61 12.03 40.34 −22.42 13.3131.46 35 Firm #3 Ex. 1 95.09 −1.5 2.04 73.95 3.26 24.36 −21.14 4.7622.32 Ex. 2 95.12 −1.51 2.19 79.74 1.27 21.72 −15.38 2.78 19.53 Ex. 395.55 −1.52 2.6 86.03 −0.46 19.67 −9.52 1.06 17.07

TABLE EIGHT Average for RULE 35 Balls L a* b* DE −23.21 13.93 31.4441.49

TABLE NINE Average for Exemplary Balls L a* b* DE −15.35 2.87 19.6425.09

As is shown in Tables Four, Five, Six, Seven, Eight and Nine, theexemplary golf balls #1, #2 and #3 of the present invention have a loweryellow measurement (b scale) before exposure, and a lower increase inyellowing after four hours and twenty four hours as compared to theCALLAWAY GOLF RULE 35 FIRMFEEL golf balls. For example, the #3 golf ballof the present invention had a b measurement of 2.6 before exposure, ameasurement of 15.78 after four hours of exposure to sunlight, and ameasurement of 19.67 after twenty-four hours of exposure. The #3CALLAWAY GOLF RULE 35 FIRMFEEL golf ball had a b measurement of 8.88before exposure, a measurement of 37.81 after four hours of exposure tosunlight, and a measurement of 40.34 after twenty-four hours ofexposure. The golf balls were exposed to sunlight on the rooftop of abuilding in Carlsbad, Calif. (latitude 32 46 30 north, longitude 117 2506 west) on a winter day. Thus, not only do the covers 16 of the golfballs of the present invention have less yellowing to begin with, afterexposure to sunlight the covers 16 yellow less than other coverscomposed of thermosetting polyurethane.

A second exemplary set of golf balls of the present invention wereprepared using polypropylene glycol terminated toulene diisocyanateprepolymer (ADIPRENE LFG960). Each of the boundary layers 14 of thesecond exemplary set of golf balls were composed of an ionomer blend offorty-five weight percent SURLYN 8150, forty-five weight percent SURLYN9150 and ten weight percent SURLYN 6350. The average thickness of eachof the boundary layers 14 of the second exemplary set of golf balls0.0525 inch, and the Shore D hardness of the boundary layer 14 was 62points. The Shore D hardness was determined according to ASTM D2240.

Each of the covers 16 of the second exemplary set of golf balls werecomposed of a polypropylene glycol terminated toluene diisocyanateprepolymer (ADRIPRENE LFG960) cured with a blend of seventy weightpercent diethyl 2,4-toluenediamine (E100) and thirty weight percent4,4″-methylenebis-(3-chloro,2,6-diethyl)-aniline (LONZACURE). Theaverage thickness of each of the covers 16 of the second exemplary setof golf balls was 0.030 inch and the Shore D hardness of the covers 16was 51 points. The COR at 143 feet per second of each of the secondexemplary set of golf balls was 79.42 points.

From the foregoing it is believed that those skilled in the pertinentart will recognize the meritorious advancement of this invention andwill readily understand that while the present invention has beendescribed in association with a preferred embodiment thereof, and otherembodiments illustrated in the accompanying drawings, numerous changes,modifications and substitutions of equivalents may be made thereinwithout departing from the spirit and scope of this invention which isintended to be unlimited by the foregoing except as may appear in thefollowing appended claims. Therefore, the embodiments of the inventionin which an exclusive property or privilege is claimed are defined inthe following appended claims.

What is claimed is:
 1. A golf ball comprising: a core; and a coverformed over the core, the cover composed of a thermosetting polyurethanematerial formed from reactants comprising a polypropylene glycolterminated toluene diisocyanate prepolymer with a NCO content rangingfrom 3.0% to 6.0% and 4,4′-methylenebis-(3-chloro,2,6-dimethyl)-aniline,wherein the cover has an aerodynamic surface geometry thereon.
 2. Thegolf ball according to claim 1 further comprising at least one boundarylayer disposed between the core and the cover.
 3. The golf ballaccording to claim 2 wherein the boundary layer is composed of a blendof ionomers.
 4. A golf ball comprising: a core; and a cover formed overthe core, the cover composed of a thermosetting polyurethane materialformed from reactants comprising a polytetramethylene ether glycolterminated toluene diisocyanate prepolymer with a NCO content rangingfrom 3.75% to 7.0% and 4,4′-methylenebis-(3-chloro,2,6-diethyl)-aniline,wherein the cover has an aerodynamic surface geometry thereon.
 5. A golfball comprising: a core comprising a polybutadiene mixture; a boundarylayer formed over the core, the boundary layer comprising at least oneionomer material; and a cover formed over the boundary layer, the covercomposed of a thermosetting polyurethane material formed from reactantscomprising a polypropylene glycol terminated toluene diisocyanateprepolymer and 4,4″-methylenebis-(3-chloro,2,6-diethyl)-aniline, whereinthe cover has an aerodynamic surface geometry thereon.
 6. The golf ballaccording to claim 5 wherein the thermosetting polyurethane material ofthe cover has a Shore D hardness ranging from 30 to 60 as measuredaccording to ASTM-D2240.
 7. The golf ball according to claim 6 whereinthe cover has a thickness ranging from 0.015 inch to 0.040 inch.
 8. Agolf ball comprising: a core; and a cover formed over the core, thecover composed of a thermosetting polyurethane material formed fromreactants comprising a polypropylene glycol terminated toluenediisocyanate prepolymer and a curative composed of4,4″-methylenebis-(3-chloro, 2,6-diethyl)-aniline and diethyl2,4-toluenediamine, wherein the cover has an aerodynamic surfacegeometry thereon.
 9. A golf ball comprising: a core comprising apolybutadiene mixture; a boundary layer formed over the core, theboundary layer comprising a blend of ionomer materials; and a coverformed over the boundary layer, the cover composed of a thermosettingpolyurethane material formed from reactants comprising a polypropyleneglycol terminated toluene diisocyanate prepolymer and a curativecomposed of 4,4′-methylenebis-(3-chloro,2,6-diethyl)-aniline and diethyl2,4-toluenediamine, wherein the cover has an aerodynamic surfacegeometry thereon.
 10. The golf ball according to claim 9 wherein thegolf ball has a PGA compression ranging from 70 points to 100 points.11. The golf ball according to claim 10 wherein the core has a PGAcompression in the range of 55 points to 80 points.
 12. The golf ballaccording to claim 10 wherein the blend of ionomer materials of theboundary layer is composed of a sodium neutralized ethylene/methacrylicacid, a zinc neutralized ethylene/methacrylic acid and a magnesiumneutralized terpolymer of ethylene, methacrylic acid and n-butylacrylate.
 13. The golf ball according to claim 10 wherein thethermosetting polyurethane material of the cover has a Shore D hardnessranging from 30 to 60 as measured according to ASTM-D2240.
 14. The golfball according to claim 10 wherein the cover has a thickness rangingfrom 0.015 inch to 0.040 inch.
 15. A golf ball comprising: a corecomprising a polybutadiene mixture, the core having a diameter rangingfrom 1.35 inches to 1.64 inches and having a PGA compression rangingfrom 50 to 90; a boundary layer formed over the core, the boundary layercomposed of a blend of ionomer materials, the boundary layer having athickness ranging from 0.020 inch to 0.075 inch, the blend of ionomermaterials having a Shore D hardness ranging from 50 to 75 as measuredaccording to ASTM-D2240; and a cover fanned over the boundary layer, thecover composed of a thermosetting polyurethane material formed fromreactants comprising a polypropylene glycol terminated toluenediisocyanate prepolymer and a curative composed of 20 to 40 parts4,4′-methylenebis-(3-chloro,2,6-diethyl)-amine and 80 to 60 partsdiethyl 2,4-toluenediamine, wherein the cover has a Shore D hardnessranging from 30 to 60 as measured according to ASTM-D2240, a thicknessranging from 0.015 inch to 0.040 inch, and an aerodynamic surfacegeometry thereon.